Two functions of PHP: generating serial numbers and string replacement

/**
* Serial number generator
 func: snMaker
 param: $pre = ''
*/
function snMaker($pre = '') {
$date = date('Ymd');
$rand = rand(1000000,9999999);
$time = mb_substr(time(), 5, 5, 'utf-8');
$serialNumber = $pre.$date.$time.$rand;
// echo strlen($serialNumber).'';
return $serialNumber;
}
echo snMaker();
/**
* Replace part of a string with a specific character
* @param str or int $str The string to be processed
* @param str or int $to What string will be replaced?
* @param int $start Keep the first few characters
* @param int $end Keep the last few characters
* url: http://bbs.it-home.org
* date: 2013/2/17
*/
function hideString($str = 'hello', $to = '*', $start = 1, $end = 0) {
$lenth = strlen($str) - $start - $end;
$lenth = ($lenth < 0) ? 0 : $lenth;
$to = str_repeat($to, $lenth);
$str = substr_replace($str, $to, $start, $lenth);
return $str;
}
echo hideString();
?>